Permanent magnet couplers of the general type disclosed in U.S. Pat. No. 5,477,094 have a magnet rotor and conductor rotor interacting to transmit power between input and output shafts. The magnet rotor has a plurality of circumferentially spaced permanent magnets having their opposite poles separated by air gaps from electro-conductive conductor elements provided by the conductor rotor on opposite axial sides of the magnet rotor. For many applications it is preferred that there be a "soft start" at start up, meaning that initially during start up there is a noticeable rotational slip between the rotors which gradually reduces to a minimum in a few seconds as the output shaft builds up speed from zero to a maximum. Less starting torque is required to drive a given load if the coupler is matched to the load such that there is a soft start experienced during start up. Also, there is less shock to the power transfer system when soft start is provided.
It is preferred that the soft start of a coupler be adjustable and that this be readily accomplished in the field after installation of the coupler. This permits a given magnetic coupler to be suitable for maximum performance in a variety of load applications without a need to change the number of magnets in the magnet rotor or change the air gaps. It also makes it possible to field adjust soft start of a coupler if the load at the installation is changed.
One approach to achieving soft start permanent magnet couplers is to vary the air gaps between the magnets on the magnet rotor and the conductor elements on the conductor rotor in a manner that can be easily accomplished at the use site without disconnecting the coupler, moving the prime mover or load, or loosening or adjusting hubs. However, this has required that the magnet rotor have two coaxial rotor components that are slide-mounted relative to the hub of the magnet rotor such that they can be moved axially relative to one another toward and away from the axially-spaced conductor elements on the conductor rotor so as to vary the air gaps equally between the conductor elements and magnets, and thereby vary the soft start.